1. Field of the Invention
The present invention relates to control of earth movement, more specifically to a retaining wall system which takes maximum advantage of earth loading and friction for long term structural stability, and low cost installation.
2. Description of the Prior Art
A typical retaining wall is usually constructed with a plurality of similar modules. Each module is designed to be held in place by anchoring to or within the earth behind the wall. The module stacks upon another module to build up wall height, and is installed adjacent to another to build wall width. The module is made of plain or reinforced concrete for the weight that it provides, and for the relatively low cost for the size and mass that it provides.
U.S. Pat. No. 770,844, patented Sept. 27, 1904 by W. L. Church, describes a retaining wall which includes a forward, upright wall joined along the length of its base by a horizontal bottom wall. A series of parallel, spaced, upright buttress walls, each of which is perpendicular to the upright and bottom walls are joined to the upright and bottom walls.
Tension rods molded into the buttress walls along the upper edge and rear edge margins of the buttress walls, meet at an apex opposite to the apex formed by the joining of the forward and bottom walls, and extend into and anchor in the upper margins of the forward walls and rearward margins of the bottom walls.
In installation, material of the retained embankment rests against the rearward surfaces of the forward, upright wall, the upward surface of the bottom wall, and exposed surfaces of the buttress walls.
The portion of each buttress which runs between the apex of the general meeting of the tension rods and the apex of the meeting of the meeting of the forward and bottom walls acts as a compression strut between these two opposed apices.
U.S. Pat. No. 4,668,129 patented by Babcock et al. on May 26, 1987, discloses a wall assembly of precast concrete modules comprised of independent elements.
The front of each module includes at each end, a vertical column portion that is attached to a vertically oriented, rearward depending triangular buttress wall. The bottom of the buttress is supported along its length by a narrow, flat, horizontally oriented base.
The front of the module comprises a vertical wall panel which rests, unattached, at each end respectively upon one of the two columns.
In assembling the wall, earth is piled behind the front of a first base tier module, over the buttresses and base and against the vertical wall panel, to a level that is slightly below the top of the vertical column portion. In the base tier module, the vertical wall panel rests at each end upon the horizontal base of the buttresses.
Further retainer wall height is attained by resting a second module that is configured for building height, on the new earth level that is slightly below the top of the vertical column portion. The wall of the second module is supported by the columns of the first module as described above. The wall of the second module is not attached to the buttresses or their bases, but is free to move as it rests upon the columns.
Each base of the second module stops short of the column that is attached to the buttress to which it is joined. A downward facing gap therefore is defined by edgewise surfaces of the column, the buttress and the base. When the second module is stacked over the first module, installed on the earth fill behind the first module, the gap allows the top of the column of the first module to extend up onto the gap without binding so that the vertically disposed tiers formed by the stacked modules can move independently.
The column portions have a battered configuration so that they form a "ship lap" type of configuration when the modules are stacked.
The ability of the stacked elements for slight relative movement between vertical tiers helps to reduce bearing stress on soil below the base portions by creating arching in the soil. This reduces necessary length of the base and buttress compared to the height of the tier that is established by the module.
U.S. Pat. No. 4,684,294, patented Aug. 4, 1987 by R. J. O'Neill, describes a precast concrete module having a rectangular upstanding front wall, and a rearward depending buttress or beam in the form of an upstanding wall joined to the center of the front wall in the form of a "T" as viewed from the top.
A side of the buttress wall includes lengthwise rectangular indentations which become filled with earth when the buttress is covered with earth to anchor the module in the embankment that it retains. The buttress wall includes a sloped rear end with a V shaped vertical groove for additional frictional engagement with the soil.
In the bottom tier, the front wall rests lengthwise upon a first horizontal rectangular concrete footer, and the buttress wall rests upon a second, transverse, rectangular, horizontal footer that is generally parallel to the first footer. A notch is provided in the bottom edge of the buttress wall to accommodate a portion of the vertical thickness of the second footer.
The top and bottom edges of the front wall include complementary lips for engaging when the modules are stacked one above another.
The buttress wall includes a notch on the top for receivng a transverse bar that is also received in the bottom notch of a buttress wall of the next tier up. The transverse bar, which extends a small distance to either side of the buttress wall, provides resistance to shear between stacked modules, and binds in the soil to resist by a fulcrum effect, rotation of the module.
When it is desired to locate the modules of an upper tier between those of the lower tier, wherein an upward T falls between two lower T's, the transverse bar extends across two modules to support the buttress of the middle T.
U.S. Pat. No. 4,804,299 patented Feb. 14, 1989 by Forte et al., describes a modular wall assembly which includes a series of horizontally spaced, vertical posts. Each post, presenting an H configuration in cross section, is embedded in the ground for about half of its length. The face of the wall is completed by panels between the posts, each panel extends at each end into a groove of the H configuration, and is embedded into the ground for about half of the depth of that attained by the posts.
Horizontal, open grids of polymeric material for further anchoring the wall to the soil are attached to the back of the panel at different heights on the panel by thermal bonding to reinforcement grid molded within the panel, or to hooks which are attached to reinforcement grid within the panel.
During installation, the earth to be retained behind the wall is graded to the level at which the lower of the grids will be laid. The grid is then covered with earth to the wall up to the level at which the next uppermost grid is to be laid. Grading, laying and covering continues until all grids to be laid are in place.